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I changed out my optical drive in my late 2006 17" iMac and before putting the front cover on it I powered it up, tried a dvd to test, shut it down and put the front cover on. With the cover on it won't power up anymore. No noise, image, light, nothing. I took the cover off and tried it again and it worked fine...cover back on...dead. I carefully put the cover on a third time with it booted up and it was ok until I pushed in on the apple. Went dead again like I pulled the plug. Only thing I could think of is this little board right behind the apple. Looks like it's spring loaded and might be misaligned. I'm curious what that board is for and if that could be my problem.

That board appears to be the Inferred board. That should not be causing your issue. When you put in the optical drive did any wires get pinched? Is the shielding back on covering everything in that bottom front area? Something is shorting or getting pinched somewhere.

You're right about the infrared board. It sits in there a little crooked and springy so I'll have to look again at that plus misplaced or pinched wires but I work pretty carefully as a rule. As far as the insulation goes the adhesive on the edges has lost much of it's stick so I added some cellophane tape to hold it in place. Maybe the wrong place..i'll look again at that. What seems strange to me is with the computer up and running with the cover off I watched half a movie no problems. While it was still running I very carefully put the cover back on including iSight harness and it stayed on fine until I squeezed the bottom together a little bit near the apple. Something is definitely out of place and I'll have to spend some more time on it tomorrow. Too late, now, but thanks very much for your valuable input. Always helps to be able to talk things like this over with someone who knows what they're talking about.

Well, I spent another hour on it before turning in looking for loose, pinched or otherwise errant wiring..didn't see anything obvious. I did notice that with the cover off and the big black flap lifted away all is well. If I lower the flap only far enough for it to touch the big heat sink next to the infrared board it shuts down immediately like you pulled the plug. It's like there shouldn't be metal to metal contact right there but there is no insulation to prevent it. There is a small mylar sticker on the flap for the infrared but it doesn't keep the metastasized flap away from the heat sink. It's like it's providing a ground path for something it shouldn't be. Any thoughts on how that flap should be tucked in or insulated? Do those small cloth covered foam rubber blocks around the edges have some electrical (grounding) function along those lines because one came loose and I'm not sure where it goes? I'm trying to find a service manual download now that may have some good illustrations.

Diligence paid off. I decided to take the logic board out just to see if there was a stray screw lodged somewhere since some were missing. I was right about that IR board but didn't know why. There is supposed to be a grounding tab sticking up from the IR board mounting screw but it was missing just like two or three screws. When I took the infrared board off in order to remove the speaker harness I found the missing tab. It was mounted on the BOTTOM of the IR board wedged up against the back of the memory slots. That must have made that heat sink 'hot' and when the shielding touched it it shorted out & shut it down. Glad it didn't blow anything out. I'm starting to think this machine was tinkered with by a non techy type or was assembled in a hurry from parts. I found a $10 Apple teardown manual download which was a tremendous help. Anyway, it works fine now, didn't cost much and I'm tickled. Thanks again.